Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum. Example 1: Input: nums = [-2,1,-3,4,-1,2,1,-5,4] Output: 6 Explanation: [4,-1,2,1] has the largest sum = 6. Example 2: Input: nums = [1] Output: 1 Example 3: Input: nums = [5,4,-1,7,8] Output: 23 Constraints: 1 <= nums.length <= 3 * 104 -105 <= nums[i] <= 105 Follow up: If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.